1. Field of the Invention
This invention relates to a magnetic recording and/or reproducing apparatus such as a video tape recorder, and more particularly to an improvement of a tape stopping mechanism in a fast-forward running mode or a rewinding running mode at a high speed.
2. Prior Art
In a magnetic recording and/or reproducing apparatus such as a video tape recorder, it is occasionally required to stop tape reels during a fast-forward running or a rewinding running of a tape. In accordance with recent high-speed tape running in a fast-forward running mode or a rewinding running mode, it becomes important to stop tape-running safely without causing slack and/or damage of a tape.
In a conventional magnetic recording and/or reproducing apparatus winding a tape at a comparatively low speed in a fast-forward running mode or a rewinding running mode, a tape stop operation is performed during a fast-forward running and a rewinding running by turning off an electric source of a drive motor and applying a strong braking force to two reels simultaneously and quickly by means of a mechanical braking means.
Such braking force is applied to each reel mechanically by shifting a position of a mechanical braking means provided on each reel and the braking properties thereof are not affected by a tape position, a direction of a tape running, and a rotation number of a capstan motor, so that a constant braking force is applied to reels.
When a rapid braking operation is performed only by the aforementioned mechanical braking means during a high-speed tape running in a fast-forward running mode or a rewinding running mode, there occur such problems that an abnormal tension is applied to a tape and/or a running tape protrudes from a predetermined running path into an inside of an apparatus due to a slight timing difference of a braking operation applied to a supply reel and a take-up reel. In order to solve the above problems, there has been proposed an improved braking mechanism having different properties depending on the rotating direction of a respective reel. For example, there has been provided a braking mechanism whereby a tape winding is so controlled that a winding amount of a take-up reel is larger than a supply amount of a supply reel by applying a strong braking force to a supply reel and applying a weak braking force to a take-up reel.
In recent high-speed tape running in a fast-forward running mode or a rewinding running mode, a rotation number of a drive motor for rotating a reel is increased and thereby a rotational inertia of the drive motor is also increased. Accordingly, when a tape stop operation is performed by turning off an electric source of a drive motor and applying a mechanical braking force during a high-speed winding mode, a take-up reel connected to a drive motor by means of a transferring mechanism such as an idler gear continues to rotate in a tape winding direction by a great rotational inertia of a drive motor, thereby applying an abnormal tension to a tape. In order to solve such problems, there has been proposed a tape stopping apparatus, in which a reverse braking force is generated by applying a rotational force to a drive motor in a direction reverse to a current rotational direction and applying a braking force to a supply reel connected to a transferring mechanism such as an idler gear. Said reverse braking force is applied to a drive motor in approximately three different manners depending on a tape position.
Said reverse braking force, however, is constant in each braking manner, so that the rotation of a take-up reel caused by a rotation inertia occasionally exceeds the rotation of an idler gear when the rotation of a drive motor is rapidly reduced. In such a case, there occurs an improper engagement of an idler gear with a gear formed on a take-up reel base, thereby causing a so-called xe2x80x9cidler squeakingxe2x80x9d phenomena, namely a squeaking trouble between an idler gear and a take-up reel base gear.
It is therefore an object of the present invention to provide a safe tape stopping mechanism eliminating the above-mentioned problems such as xe2x80x9cidler squeakingxe2x80x9d caused by a rotation inertia of a take-up reel, tape protrusion caused by a rapid braking operation and a tape damage caused by an abnormal tension applied thereto.
The inventors have made various investigations in order to solve the above problems and found that such problems can be eliminated by employing a tape stopping mechanism wherein a braking force is applied to a supply reel and a take-up reel by means of a mechanical braking means and also by applying an reverse braking force of a drive motor in accordance with the rotation number of a drive motor in such a manner that the lower the rotation number of a drive motor is, the smaller the reverse braking force is.
The reverse braking force is decided in accordance with the braking force of a mechanical braking means. In addition thereto, it is preferable that the reverse braking force is decided so as to be in inverse proportion to a total tape area. Namely, in the case of a tape having a large total area, the ratio of a tape area of a take-up reel to that of a supply reel becomes large at the beginning of tape winding or at the end of tape winding, so that the rotational inertia of a supply reel is increased when a fast-forward running is stopped at the beginning of tape winding or a rewinding running is stopped at the end of tape winding. Accordingly, when a strong reverse braking is applied, a take-up reel is immediately stopped and there occurs a tape protrusion out of a supply reel. On the contrary, in the case of a tape having a small total area, a supply reel is stopped earlier than a take-up reel, so that it is necessary to stop the take-up reel earlier by applying a strong reverse braking so as to prevent tape damages.
Accordingly, it is preferable that the reverse braking force is applied so as to be in inverse proportion to a total tape area, so that the reverse braking force is weakly applied to a tape having a large total area and strongly applied to a tape having a small total area, thereby preventing the protrusion of a tape and tape damages caused by the rotational inertia of reels. The total tape area may be calculated by detecting the rotation number of the supply reel and the take-up reel respectively using a reel rotation detecting means. The reverse braking force may be controlled so as to be reduced in proportion to the reduction of the rotation number of a drive motor, thereby reducing the reverse braking force at the beginning of tape wining and the end of tape winding and preventing the occurrence of squeaking. The reverse braking force may be reduced either by a proportional control in response to the rotation number of the drive motor or by a stepwise control. In the case of the stepwise control, the reverse braking force may be set to have three stages from a first stage to a third stage depending on the rotation number of the drive motor. The drive motor is controlled by applying a reverse braking force in response to the rotation number of the drive motor detected by a rotation detecting means and also controlled by applying a reverse braking force reduced stepwise in proportion to the reduction of the rotation of the drive motor. The rotation number of the drive motor may be detected by using a frequency generator (FG) which generates a frequency signal depending on the rotation number of the drive motor.
For deciding the reverse braking force, it is preferred that the tape area of a take-up reel and the rotation number of the drive motor is taken into account so as to apply the reverse braking force depending on the rotational inertia of reels. The reverse braking is for preventing the rotation inertia of the take-up reel, so that the reverse braking force should be increased in proportion to the increase of the rotational inertia of the take-up reel. In general, an inertia is in proportion to the product of a weight and the square of a speed. Assuming that a weight is a tape area of the take-up reel and a speed is the rotation number of a drive motor, the reverse braking force applied in proportion to the tape area of the take-up reel and the rotation number of the drive motor can be matched the rotational inertia of a drive motor. The tape area is calculated by detecting the rotation number of the supply reel and the take-up reel respectively using a reel rotation detecting means as in the case of detecting the total tape area.
Furthermore, when the reverse braking force is so controlled to be reduced at the beginning of the tape winding or the end of the tape winding by detecting a total tape area and a tape area of the take-up reel and calculating the ratio of the tape area to the total tape area, tape damages can be effectively prevented.